This invention relates generally to duplicating machines and, more particularly, to a sheet feeding mechanism for use in a machine for duplicating images on both sides of copy sheets, hereinafter sometimes referred to as "duplexing".
Duplicating machines are available for the production of copies with images formed on one side of the copy sheets. Such equipment can be reliably operated at highly satisfactory production rates. Because of the advantages of duplexing in savings of the amount of paper employed, savings in the space occupied by the copies produced, and savings in production time and equipment costs, it is desirable to provide machines for imaging both sides of a copy sheet.
Duplexing often is effected by duplicating machines employing a single printing couple to thereby provide a compact unit that may be utilized in small work areas and conserve the amount of floor space required in which to operate the equipment. However, single printing couples for duplex printing require relatively large and expensive master cylinders, blanket cylinders and impression cylinders because of the multiple images required on a single cylinder. Sometimes the cost is prohibitive. In addition, relatively complex gripper mechanisms are required on the impression cylinder, as well as complex mechanisms for handling sheets released from the impression cylinder and for re-feeding the sheets back to the gripper mechanisms on the cylinder. Such complex machines are not capable of high speed duplexing.
Consequently, it is desirable to utilize plural printing couples employing less expensive cylinders and gripper mechanisms where the work area or floor space in which the machine is to be utilized is not a premium. The plural printing couples can be arranged in tandem or straight-line configurations or in known L-shaped configurations. Regardless of the configuration or arrangement of the plural printing couples, sheet handling mechanisms are required for passing a copy sheet through a first printing couple for imaging one side of the sheet and advancing the sheet to a second printing couple for imaging the opposite side of the sheet.
One of the problems in duplexing machines utilizing plural printing couples is that the sheet handling mechanisms between the first and second printing couples must be designed to only engage the first imaged side of the copy sheets along the side edges thereof to preclude ink contamination, commonly termed "tracking". A particular sheet handling mechanism is disposed at the entrance end of the second printing couple. As with most printing couples employed in common duplicating machines, sheets are advanced seriatim to stop means where the sheets are aligned preparatory to feeding through the printing couple. Once aligned, feed rollers are intermittently operated to advance the sheets seriatim through the printing couple in unison with rotation of the various imaging cylinders. In a duplexing machine employing plural printing couples, one side of each copy sheet already has been imaged when transferred to the second printing couple. Therefore, feed roller assembies must be provided to preclude tracking the first image on one side of the sheet.
Heretofore, the feed roller assembly at the entrance to the second printing couple comprised a lower impression cylinder extending laterally across the path of and beneath the copy sheets. A pair of side feed rollers were movable toward and away from the pressure roller to intermittently feed the sheets to the second printing couple. The side feed rollers were mounted on a cylindrical shaft extending between a pair of side braces or supports. The feed rollers were adjustable axially of the shaft to accommodate different sheet sizes. However, the side braces or supports preclude the feed rollers from moving axially outwardly of the shaft beyond the braces. The braces themselves could not be moved outwardly of the shaft because of the normal confines of the machine, including its exterior frame. Therefore, sheets could not be imaged close to the extreme marginal edges thereof without the feed rollers causing tracking of the images transferred to the sheet by the first printing couple.
There is a need for a new feed roller mechanism which permits adjustment to position the side feed rollers near the marginal edges of the copy sheets. This invention is directed to solving this need by providing a new and improved sheet material feeding mechanism for duplexing machines, particularly a new feed roller assembly at the entrance end of a second printing couple in a duplex duplicating machine.